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When a failed bearing brings a drone motor, RC car drivetrain, or precision instrument to a halt, finding the exact replacement in the right bore size matters. Engineers, hobbyists, and repair technicians working with compact rotating assemblies need miniature deep groove ball bearings that fit precisely and run quietly without adding bulk to tight spaces.
This listing covers two complementary series of miniature deep groove ball bearings: the 628 series (ZZ double-shielded, bore 2–9mm, OD 5–17mm, width 1.5–5mm) and the 618 series (open and ZZ shielded, bore 1–9mm, OD 3–17mm, width 1–4mm). Both series feature steel construction with precision-ground raceways. Available individually or in packs of 3, 5, or 10 pieces.
Typical use cases include miniature DC motor shaft support in RC vehicles and drones, spindle bearings in 3D printer extruder assemblies, pivot points in precision measuring instruments, and small gearbox idler shafts in robotics. The ZZ shield variants reduce contamination ingress in dusty workshop environments, while open variants suit applications requiring lubrication access.
| Series | 618 series (open & ZZ), 628 series (ZZ) |
|---|---|
| Bore Diameter (d) | 1mm – 9mm (see variant options) |
| Outer Diameter (D) | 3mm – 17mm (see variant options) |
| Width (B) | 1mm – 5mm (see variant options) |
| Shield Type | ZZ (double steel shield) or Open — see variant name |
| Material | Steel (raceway & rolling elements) |
| Dimensional Standard | ISO 618 / ISO 628 series |
| Available Quantities | 1 pc, 3 pcs, 5 pcs, 10 pcs |
| Lubrication (ZZ models) | Factory-greased, sealed by steel shields |
| Lubrication (Open models) | See variant options / Contact us to confirm |
| Operating Temperature | See variant options |
| Radial Load Rating | See variant options |
The key difference is the width-to-bore ratio. The 628 series is slightly wider relative to its bore — for example, a 628/6-ZZ measures 6×13×5mm, while a 618/6-ZZ measures 6×13×3.5mm. If your housing depth is constrained, the 618 series offers a thinner profile at the same bore and OD. If you need more load capacity in the same bore size, the wider 628 series is the better choice. Always check the B (width) dimension against your housing depth before ordering.
ZZ indicates that the bearing has steel shields pressed onto both sides of the outer ring. These shields reduce the entry of dust and debris into the raceway and help retain the factory-applied grease. ZZ bearings are not fully sealed — they are not rated for submersion — but they perform well in dry, dusty, or lightly contaminated environments. Open variants (no suffix) have no shields and allow direct lubrication access.
Yes. Both the 618 and 628 series follow ISO dimensional standards, so bore, outer diameter, and width match the published ISO tolerances for these series. This means they are dimensionally interchangeable with other ISO-compliant 618/628 bearings of the same model number. Verify the three dimensions (d×D×B) listed in the variant name against your application before ordering.
Miniature deep groove ball bearings in the 618 and 628 series are commonly used in brushless drone motors and high-speed spindles. The ZZ-shielded variants retain grease at elevated RPM and resist contamination from rotor wash. For specific speed ratings (limiting speed / reference speed), refer to the ISO 618/628 series load tables for the exact model number, as these vary by bore size and bearing width.
Single pieces (1 pc) are suited for one-off repairs or prototyping. Packs of 3 or 5 are practical for small builds with multiple bearing positions — for example, a 3D printer with two Z-axis lead screw bearings and one extruder bearing. Packs of 10 offer the lowest per-unit cost and are recommended if you maintain a service stock or are building multiple units of the same design.
ZZ-shielded models come factory-greased and are ready to install without additional lubrication. Do not wash or re-lubricate ZZ bearings before installation, as this can displace the factory grease. Open variants (618/1, 618/2, 618/3 — no ZZ suffix) should be lightly lubricated with a suitable bearing grease or oil appropriate for your operating speed and load before installation.
The smallest model is the 618/1, with a 1mm bore, 3mm outer diameter, and 1mm width. This is one of the smallest standard deep groove ball bearings available and is used in micro-motors, precision instruments, and miniature robotics joints where shaft diameters are 1mm.
